[asterisk-bugs] [Asterisk 0010274]: T.38 passthrough with 2 Asterisk boxes not working

[noreply at bugs.digium.com]

A NOTE has been added to this issue. 
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http://bugs.digium.com/view.php?id=10274 
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Reported By:                cstadlmann
Assigned To:                
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Project:                    Asterisk
Issue ID:                   10274
Category:                   Channels/chan_sip/T.38
Reproducibility:            always
Severity:                   block
Priority:                   normal
Status:                     new
Asterisk Version:            SVN 
SVN Branch (only for SVN checkouts, not tarball releases):  1.4  
SVN Revision (number only!): 76410 
Disclaimer on File?:        N/A 
Request Review:              
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Date Submitted:             07-23-2007 08:41 CDT
Last Modified:              07-30-2007 10:38 CDT
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Summary:                    T.38 passthrough with 2 Asterisk boxes not working
Description: 
This is the configuration I'm using:

ATA 1 <-> Asterisk 1 <-> Asterisk 2 <-> ATA 2

As long ATA's are resided on the same Asterisk box, no T.38 problem. But
if ATA 1 is trying to send a fax via T.38 to ATA 2, the complete call fails
because Asterisk 1 is killing it during re-invite and Asterisk 2 gives up.

Both Asterisk boxes are: SVN-branch-1.4-r76410
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Relationships       ID      Summary
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has duplicate       0010317 Bug 10274 seems to be SIP related, not ...
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 putnopvut - 07-30-07 10:38  
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Just so you don't think no one's looking at this, I'll put in my thoughts.
Keep in mind that I'm still learning SIP and so what I say may or may not
be right.

It appears that the re-invite sent from ATA2 is reaching ATA1 properly.
There are other problems along the way that need to be addressed.

1. It would appear that Asterisk2 is expecting to receive a response to
the re-invite it transmits, such as possibly a 100 trying. Since it's not
receiving such a response, it continues retransmitting the re-invites.
Should Asterisk1 (or for that matter, Asterisk2) be generating provisional
responses to the re-invites?

2. Let's say that Asterisk shouldn't be generating the provisional
responses in point 1 above, and so Asterisk2 should be generating all the
retransmissions. Even so, RFC3621 specifies that if a UAS receives a
reinvite for an INVITE already in progress, it should send a 491 response.
In this case, Asterisk1 is not sending the 491 to Asterisk2 and in fact is
deferring the re-invites for later. This is why that call to check_pendings
you mentioned is causing Asterisk1 to send a re-invite to ATA1, and it
could also be why the passthrough fails later when you removed the call to
check_pendings.

So in summary, it seems that T38 negotiation fails due to lack of expected
responses being generated for reinvites. Thoughts? 

Issue History 
Date Modified   Username       Field                    Change               
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07-30-07 10:38  putnopvut      Note Added: 0068059                          
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